The invention is concerned with the stiffening of a surface portion of a flexible roof skin of a vehicle of the type comprising a reinforcing section arranged at the roof skin and matched flexurally elastically to a curve of the roof skin in the surface portion.
A stiffening of a flexible roof skin of this type is disclosed by German Patent Specification No. 2,327,485, wherein the insertion of a spring-steel strip into the roof skin of a folding hood underneath the rear triangular panes of the roof makes it possible for the flexible triangular panes to always fold uniformly. Since only a front length portion of the triangular panes is stiffened with the spring-steel strips, the folding line of the flexible triangular panes extends exactly behind the stiffened length portion. The stiffening effect of the spring-steel strip on the flank region of the roof skin is very limited and makes no appreciable contribution to preventing roof skin fluttering which occurs at high driving speeds when the roof is closed and which is caused by the airflow breakaway or separation at the rear region of the roof skin. However, this effect of roof skin fluttering is associated with the generation of relatively loud noise and is therefore detrimental to driving comfort. If the flexible panes of the roof skin are likewise influenced by this effect, there are, in addition, optical distortions which can impair vision at the rear.
An object of the present invention is, therefore, to provide a further stiffening of a surface portion of a flexible roof skin of a vehicle, in such a way that the effect of roof skin fluttering is markedly reduced over a surface portion of larger size.
This objective is achieved by the invention by providing a tensioning device for subjecting a reinforcing section of the roof skin to stress in such a way that the reinforcing section can be changed from a bent position to a more sharply curved tensioning position when the roof skin is closed. As a result the tension of the roof skin in the stiffened region is markedly increased over and above the basic tension by a hood frame.
Various tensioning devices which are preferably supported on the frame are contemplated by the invention for obtaining the associated curving of the reinforcing section.
No additional operating outlay is involved in an automatic activation of the tensioning device.
Especially simple curving of the reinforcing section is possible if both ends of the latter are subjected to an axial advance which results in more pronounced bending of the reinforcing section. At the same time, depending on the material of the roof skin, the reinforcing section can experience free deformation over its length, either together with the roof skin, between end clamping points or there can be on the roof skin a sliding guide which allows the reinforcing section to undergo longitudinal displacement relative to the roof skin.
Appropriately, the axial advance is transmitted to the reinforcing section purely mechanically via supporting frame parts in the course of the closing operation.
An especially simple, inexpensive and lightweight embodiment of the tensioning device is possible as a result of pulling means, such as wire cables or the like.
Thus, even several reinforcing sections can be changed to their tensioning positions simultaneously by two pulling means, so that a tensioning framework for rear windows, which does not impair the folding of these, can be formed very economically.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.